Stabilizing cation resins

ABSTRACT

Polyvinyl aryl sulfonate resins are stabilized against sulfonate leakage by leaching with water at a temperature of about 340* to 400* F. for at least about one hour to remove weakly held sulfonate groups. The resin may be further stabilized by converting about 5 to 30 percent of the ion exchange sites to the divalent or polyvalent metal form; preferably the barium or calcium form.

United States Patent [191' Ryan [ 1 Feb. 20, 1973 [54] STABILIZINGCATION RESINS [75] Inventor:

[73] Assignee: Ecodyne Corporation, Chicago, Ill.

[22] Filed: Jan. 19, 1970 21 Appl. No.: 4,119

Leo F. Ryan, Somerville, NJ.

[52] [1.8. CI. ..260/2.2 R, 210/38 [51] Int. Cl ..B0ld 15/06, C021) H76[58] Field of Search ..260/2.2

[56] References Cited FOREIGN PATENTS OR APPLICATIONS 42,920 2/1966Germany 185,052 7/1966 U.S.S.R.

OTHER PUBLICATIONS Koganovskii et al., Ukr. Khim. Zh. 1968, 34, 446-449(abstr. supplied) Brown, Effluent Water Treat. J. 1968, 8, 394-400(abstr. supp.)

Sednev et al., Geterogennye .Reaktsii i Reakts. Sposobnost, Sb. 1964,20-25 (abstr.)

Helfferich, Ion Exchange, McGraw-Hill, New York, 1962 (p. 168) PrimaryExaminer-Melvin Goldstein Attorney-Hume, Clement, Hume & Lee, Charles M.Kaplan and Brinks, Wetzel, William, Cook, Clark, Lione, Cummins,Blanchard, l-lofer [57] ABSTRACT 11 Claims, No Drawings STABILIZINGCATION RESINS The present invention relates to a method for stabilizingcation exchange resins of the polyvinyl aryl sulfonated type.

Sulfonated polyvinyl aryl cation exchange resins are well known in theart. The preparation of such resins is described in U.S. Pat. No.2,366,007 to D'Alelio. Such resins generally comprise polymers andcopolymers of divinylbenzene with sulfonate groups substituted onto thebenzene rings. These sulfonate groups have a negative charge, andtherefore have the capability of forming cation exchange sites. Aparticularly desirable sulfonated polyvinyl aryl resin has a backbonechain that is a copolymer of styrene and divinylbenzene. Once thebackbone polymer has been prepared, it is sulfonated by the use ofconventional sulfonating agents such as concentrated sulfuric acid,fuming sulfuric acid, chlorosulfonic acid, etc. The product is thenconventionally steamed to remove the excess sulfonating agent.

While polyvinyl aryl sulfonates are highly desirable and suitable ionexchange materials in most applications, a difficulty is encounteredwhen such resins are to be employed where extreme purity of the water isrequired. Extreme purity is required, for example, in condensatepolishing processes performed on the recycle water used on steamgenerating stations. Such polishing is carried out with both cation andanion exchange resins, the cation exchange resin being in the hydrogenor ammonium form, and the anion exchange resin being in the hydroxideform. For example, a wellknown polishing process and apparatus ismarketed under the POWDEX trademark by the Graver Water ConditioningCompany. Patents related to such a process and apparatus include U.S.Pat. Nos. 3,250,703, 3,250,704 and 3,279,608, all of which are assignedto the assignee of this application. Such condensate polishing processesare frequently required to reduce the impurities in the recirculatedwater to levels not exceeding 3 parts per billion.

A difficulty that is encountered when such extreme purity levels arerequired is the contamination of the water by the leakage of sulfonateions from the resin itself. It is believed that such leakage occursprimarily because some of the sulfonate groups are more weakly held onthe resin than others. For example, some of the benzene rings may havemore than one sulfonate group, and the excess sulfonate groups are morereadily removed. This removal of sulfonate groups from the resin isincreased at the elevated temperatures that are often-encountered incondensate polishing processes.

Generally, the present invention relates to a method for stabilizingcation exchange resins of the polyvinyl aryl sulfonate type by removingexcess sulfonate groups. In carrying out the method, the resin isleached with water at a temperature of about 340 to 400 F. for at leastabout 1 hour prior to use.

More specifically it has now been found that polyvinyl aryl sulfonateresins may be stabilized by leaching with water at a temperature ofabout 340 to 400 F. for at least about 1 hour. Improved results areobtained in accordance with the preferred embodiment when this leachingstep is repeated at least twice, and wherein the resin is rinsed inwater between the leaching steps. The temperature of the rinse water isnot important, however, except that it should not be higher than about400 F. In the preferred embodiment, the temperature of the leachingwater is about 340 to 360 F. Also, for best results, it is preferredthat each leaching step be performed over a time period of at leastabout 2 hours. These leaching steps remove excess sulfonate groups fromthe resin, and substantially reduce or eliminate the leakage ofsulfonate ions into the water being treated.

It has also been found, in accordance with the most preferred embodimentof the present invention, that polyvinyl aryl sulfonate resins may beeven further stabilized by contacting the resins with cations selectedfrom the group consisting of divalent and polyvalent metal cations in anamount sufficient to convert about 5 to 30 percent of the ion exchangesites of the resin to the metal form. The preferred cations for use insuch further stabilization are barium and calcium cations.

In the preferred embodiment, the resin is contacted with sufficientdivalent or polyvalent metal cations to convert from 5 to 20 percent,and most preferably about 15 percent, of the ion exchange sites to themetal form. The percentage of the sites to be converted to the metalform depends upon a number of factors, the most important being theamount of metal leakage that can be tolerated. In condensate polishingprocesses, the metal leakage must be virtually zero. Metal leakage will,in turn, be influenced by the pH and ion concentration of the streambeing treated. Another factor that must be considered is the temperatureof the water being treated, since, as previously mentioned, the resintends to be less stable at higher temperatures. Finally, a minorconsideration is the reduction in ion exchange capacity of the resin bymetal exchange. While small reductions are not significant in condensatepolishing processes, at higher metal concentrations this reduction maybecome significant, and require frequent replacement of the exhaustedresin.

When polyvinyl aryl sulfonate resins are stabilized with divalent orpolyvalent cations subsequent to the above-described leaching step, ithas been found that the tendency of the resin .to lose sulfonate groupsis virtually eliminated. The reason why such divalent and polyvalentcations stabilize the resin is not understood, although it is believedthat these cations react with the most active sulfonate groups, and thatthese sulfonate groups are also the ones that are most likely to beremoved from the resin during ion exchange.

While the method of the present invention causes a reduction in the ionexchange capacity of the resin, this reduction is relativelyinsignificant in polishing processes such as condensate polishingprocesses where high-capacity resins are not needed. As previouslymentioned the objective is extreme purity of the water, and the waterwill ordinarily contain only very low levels of impurities when it isdelivered to the ion exchange resin.

The following examples are intended to illustrate the present invention,and should not be construed as limitative, the scope of the inventionbeing determined by the appended claims.

In the following examples, the resin used was Nalco HCR-W, a stronglyacidic cation exchange resin having sulfonate groups on astyrene-divinylbenzene copolymeric backbone chain. The resin was in the20-40 mesh bead size. This resin is marketed by the Nalco ChemicalCompany of Chicago, Illinois.

EXAMPLE I About 50 pounds of fresh HCR-W resin was treated by passing 3molar hydrochloric acid through it until it was converted to thehydrogen form. The beads were then rinsed with demineralized water untilthe conductivity of the effluent rinse water was reduced to 0.5micromhos per centimeter.

The hydrogen-form resin beads were immersed in demineralized water in anautoclave, and the autoclave contents were heated to 350 F. and held atthat temperature for 2 hours. The contents were then cooled to less than212 F., the autoclave was opened, and the resin beads were rinsed withabout 2 volumes of demineralized water. The autoclave was then refilledwith sufficient demineralized water to immerse the resin beads and wasrescaled. The contents of the autoclave were reheated to 350 F. and heldat that temperature for 2 hours. The contents were then cooled andrinsed as before. After draining, the beads were ground to a size ofabout 400 mesh for use in the Powdex process. A capacity measurement ofthe treated resin showed about a 2-4 percent loss in ultimate ionexchange capacity as compared to untreated resin of the same particlesize.

A slurry of the ground resin was titrated with an ammonium hydroxidesolution to a pH of 5 to convert the active sites to the ammonium form.The resin was then rinsed in a stream of demineralized water until theeffluent conductivity was reduced to about 1 micromho per centimeter.

EXAMPLE ll One half of the resin slurry obtained in Example I wasfurther treated by adding a weight percent solution of barium chloridein an amount which had been calculated to be sufficient to convert 18percent of the active ion exchange sites to the barium form. The slurrywas agitated to ensure complete exchange. The resin was then rinsed in astream of demineralized water until the conductivity of the effluentstream was reduced to about l micromho per centimeter.

EXAMPLE "I A 50-pound sample of fresh HCR-W resin was treated with 3molar hydrochloric acid and rinsed with demineralized water as inExample I. A slurry of the resin was then treated by adding a 10 weight.percent solution of barium chloride in an amount which had beencalculated to be sufficient to convert about 40 percent of the ionexchange sites to the barium form. The slurry was agitated during thisstep. The resin was thenrinsed in a stream of demineralized water untilthe conductivity of the effluent stream was reduced to about 1 micromhoper centimeter.

EXAMPLE IV The resins prepared in Examples [-11], together with someuntreated Nalco HCR-W resin (ground to about 400 mesh) were mixed withanion exchange resin in the ratio of 5:1 cation:anion resin by weight.The anion resin was a strong base quaternary amine resin having astyrene-divinylbenzene copolymer backbone chain, distributed and sold byNalco Chemical Company as Nalco SBRP. The resins were mixed according tothe method set forth in U.S. Pat. No. 3,277,270 to Capecci, which isassigned to the assignee of this application. The mixed resins-were thenpre-coated onto cylindrical filter elements in accordance with themethod set forth in U.S. Pat. No. 3,250,703 to Levendusky, which isassigned to the assigneeof this application. The filter elements wereeach pre-coated with 0.5 pounds of resin per square foot of filtersurface area.

Individual pilot plant studies were run with a filtration unit havingeach of the aforementioned precoats. The ammoniated heater drain from apower station, having a pH of about 9.4 was continuously passed throughthe filter cartridges at a flow rate of 4.4 gallons per minute persquare foot of filter surface area, and at a temperature of 352 F.

The acid conductivity peak of the effluent water was measured in eachinstance. This conductivity peak is indicative of the amount ofsulfonate ions introduced into the water, since leakage of these ionswill generate acid. The results are shown in the following table.

Resin Acid Conductivity Peak (micromhos per cm) Example I 0.45 Example[I 0.25 Example ll] 0.6 Untreated resin l.2

measured above reference of 0.2 micromho/cm.

Surprisingly, the heat treatment of Example I reduced the conductivitypeak by about 62 percent,.

even though the reduction in ion exchange sites was only about 2-4percent. This result indicates that the treatment of Example I removedthe most readily cleavable sulfonate groups.

The conversion of 18 percent of the active sites to 1 the barium form inExample II further reduced the conductivity to about 56 percent of itsprevious value. This result also indicates that the most readilyremovable sulfonate groups are being stabilized, since the increase instability is out of proportion to the amount of barium used. Finally, asthe results obtained with the resin of Example III demonstrate, theconversion of 40 percent of the active sites to the barium form does notproduce as significant an effect as the heat treatment alone. Becausethe conversion of such a large portion of the ion exchange sites to thebarium form reduces the ion exchange capacity and increases thelikelihood of barium leakage, the partial ion exchange of the resin witha divalent or polyvalent metal should not be performed except inconjunction with the high-temperature leaching step.

Obviously many modifications and variations of the invention ashereinbefore set forth will occur to those skilled in the art, and it isintended to cover in the appended claims all such modifications andvariations as fall within the true spirit and scope of the invention.

I claim:

1. A method for stabilizing cation exchange resin of the polyvinyl arylsulfonate type comprising: leaching said resin with water at atemperature of about 340 to 400 F. for at least about 1 hour whereby toremove weakly held sulfonate groups from said resin.

2. The method as defined in claim 1 wherein said leaching is carried outat least twice, and further including the step of rinsing said resinbetween said leachings.

3. The method as defined in claim 2 wherein the temperature of saidwater is about 340 to 360 F.

4. A method for stabilizing cation exchange resin of the polyvinyl arylsulfonate type comprising: leaching said resin with water at atemperature of about 340 to 400 F. for at least about 1 hour whereby toremove weakly held sulfonate groups from said resin; and contacting saidresin with an aqueous solution of cations selected from the groupconsisting of divalent and polyvalent metal cations in an amountsufficient to convert about 5 to 30 percent of the ion exchange sites ofsaid resin to said cation form.

5. The method as defined in claim 4 wherein said cations are selectedfrom the group consisting of barium and calcium.

6. The method as defined in claim 4 wherein said resin is contacted withan aqueous solution of said cations in an amount sufficient to convertabout 5 to percent of the ion exchange sites of said resin to saidcation form.

7. The method as defined in claim 6 wherein said cations are selectedfrom the group consisting of barium and calcium.

8. The method as defined in claim 7 wherein said cation is barium.

9. The method as defined in claim 8 wherein said resin is contacted withan aqueous solution of said barium cations in an amount sufficient toconvert about 15 percent of the ion exchange sites of said resin to thebarium form.

10. A method for stabilizing cation exchange resins of the polyvinylaryl sulfonate type comprising: leaching said resin with water at atemperature of about 340 to 400 F. for a time period of about 1 to 3hours; rinsing said resin; again leaching said resin at a temperature ofabout 340 to 400 F. for a time period of about 1 to 3 hours, whereby toremove weakly held sulfonate groups; and contacting said resin with anaqueous solution of cations selected from the group consisting of bariumand calcium in an amount sufficient to convert about 5 to 20 percent ofthe ion exchange sites of said resin to said cation form.

11. The method as defined in claim 10 wherein the temperature of saidwater is in the range of about 340 to 360 F.

1. A method for stabilizing cation exchange resin of the polyvinyl arylsulfonate type comprising: leaching said resin with water at atemperature of about 340* to 400* F. for at least about 1 hour wherebyto remove weakly held sulfonate groups from said resin.
 2. The method asdefined in claim 1 wherein said leaching is carried out at least twice,and further including the step of rinsing said resin between saidleachings.
 3. The method as defined in claim 2 wherein the temperatureof said water is about 340* to 360* F.
 4. A method for stabilizingcation exchange resin of the polyvinyl aryl sulfonate type comprising:leaching said resin with water at a temperature of about 340* to 400* F.for at least about 1 hour whereby to remove weakly held sulfonate groupsfrom said resin; and contacting said resin with an aqueous solution ofcations selected from the group consisting of divalent and polyvalentmetal cations in an amount sufficient to convert about 5 to 30 percentof the ion exchange sites of said resin to said cation form.
 5. Themethod as defined in claim 4 wherein said cations are selected from thegroup consisting of barium and calcium.
 6. The method as defined inclaim 4 wherein said resin is contacted with an aqueous solution of saidcations in an amount sufficient to convert about 5 to 20 percent of theion exchange sites of said resin to said cation form.
 7. The method asdefined in claim 6 wherein said cations are selected from the groupconsisting of barium and calcium.
 8. The method as defined in claim 7wherein said cation is barium.
 9. The method as defined in claim 8wherein said resin is contacted with an aqueous solution of said bariumcations in an amount sufficient to convert about 15 percent of the ionexchange sites of said resin to the barium form.
 10. A method forstabilizing cation exchange resins of the polyvinyl aryl sulfonate typecomprising: leaching said resin with water at a temperature of about340* to 400* F. for a time period of about 1 to 3 hours; rinsing saidresin; again leaching said resin at a temperature of about 340* to 400*F. for a time period of about 1 to 3 hours, whereby to remove weaklyheld sulfonate groups; and contacting said resin with an aqueoussolution of cations selected from the group consisting of barium andcalcium in an amount sufficient to convert about 5 to 20 percent of theion exchange sites of said resin to said cation form.